Transit of Venus Today -- Watch it Live!

For those who have any interest in astronomy or who regularly check out the Astronomy Picture of the Day, this will be very old news, but for everyone else, I wanted to get the word out that today is the last time this century that the planet Venus will pass in front of the Sun. What is special about this, you might ask? Well, this type of transit is one of the rarest astronomical events that we can predict. Pairs of transits occur separated by a period of eight years, but these pairs are separated by over a century. You may remember the last transit of Venus which occurred in 2004. But if you miss today's, you will have to wait until 2117 to see it again.

Historically, the transit of Venus is also important, because it provided one of the first somewhat accurate determinations of the Astronomical Unit (the distance between the Earth and the Sun). Many distances in astronomy can be determined by the parallax from the Earth's motion around the Sun. The distance to an object can be determined by the change in viewing angle to that object by simple geometry. However, as a result, these distances were always in terms of the change in position of the Earth, which comes from the Astronomical Unit. Also, Kepler's third law allowed scientists to determine the distances from the other planets to the Sun, but again, this was in terms of the Astronomical Unit. However, until the 17th century, no one had a good idea of how big the Astronomical Unit was. In 1639, Jeremiah Horrocks made observations of the transit of Venus which allowed him to not only estimate the size of Venus, but also to make the most accurate (until that point) estimation of the distance from the Earth to the Sun (the Astronomical Unit). (FYI, The history involved in determining the size of the AU is actually very interesting and a lot more involved than what I've given here.)

Even for those who do not have a crazy historical bent, the transit of Venus is just plain cool! (You can think of it as an extremely small annular eclipse of the Sun.) The above image is downloaded from NASA's Solar Dynamics Observatory and will update automatically through the day. For those in the United States, the transit will be visible about sunset. For visibility times and transit paths in other parts of the world, check out NASA's websites on the Transit of Veus. If you try to view the transit first-hand, make sure you remember proper solar viewing safety. Happy Viewing!

Gravitational Lensing

This semester I am the TA for the numerical techniques class offered by my department (as in I am the only TA). For the class the students have projects where they demonstrate some numerical technique by solving a somewhat more advanced problem. One of my students had a project where he was trying to show gravitational lensing. He loaded images taken by Hubble into Matlab and then calculated how the image would be warped by a black hole between us and the target. With a little help from me, and a lot of work on his part, he managed to make a short video of what the Andromeda Galaxy would look like if a black hole passed between us and the galaxy.

 

The strength of the lensing is greatly distorted (I think he assumed a black hole of > 10^12 M_sun) in order to emphasize the effect. Still it looks pretty cool.

Below are some real pictures of gravitational lensing for comparison.

Source: APOD

Source: Hubblesite.org

Kepler Finds A Possibly Live One

The Kepler mission has been looking for planets that might have liquid water (and therefore life as we know it) and it looks like they have their first confirmed candidate - the oh-so-memorably-named Kepler 22b.  Kepler 22b, or just 22b for short, has a radius 2.4 times as big as the Earth's and orbits a star that has roughly 2% less mass than the Sun every 289 days. That places it right at the inner edge of that star's habitable zone (the range of distances from their star where planets might have liquid water), as illustrated by this lovely NASA graphic.

If you assume an Earth-like greenhouse effect for 22b (which is a big assumption considering Venus and Mars have drastically different atmospheres than Earth), the mean surface temperature (assuming it has a surface) would be a balmy but not unreasonable 22 degrees Celsius compared to Earth's mean surface temperature of about 14 degrees Celsius.

NASA likes to call this type of planet a "Super-Earth", however that's something of a misnomer as planets with more than twice the radius of Earth probably aren't primarily rocky planets like Earth, Venus, and Mars but rather more like smaller, defrosted versions of our solar system's ice giants, Neptune and Uranus.  Using planetary structure models, one can map out the range of possible compositions for a planet of a given radius (remember with Kepler's transit data they know the planet's size but not it's mass).

As you can see, 22b likely has a composition with significant amounts of hydrogen and helium, which means it may have a very thick, deep atmosphere. Alternatively it could have very large amounts of water, but at this point there's just no way to tell what it's made of as the planet is too far from it's star to be detected using the radial velocity technique, which can determine a planet's mass.  It's possible that space telescopes like Hubble and Spitzer might be able to get some information on the composition of the planet's atmosphere, but most likely this one is going to have to wait for new telescopes and instruments to be characterized more fully.

The best part is that 22b is not alone.  The Kepler team only officially announces a planet as discovered when they can confirm it using another telescope (here they used Spitzer to verify a transit), but the list of "planet candidates" in habitable zones is growing.  As of the now, there are about a half-dozen planet candidates in habitable zones that are smaller than 22b. 

As Kepler approaches it's third anniversary, expect those numbers to increase dramatically.  You can already see the trend by comparing the numbers of planets from the June 2010 (in blue), February 2011 (in red), and December 2011 (in yellow) data releases.

You can find the official NASA press release here and the slides from that press release (which are the source of these lovely images) here.

Yahoo! Makes Black Holes Hip

Disclaimer:  As a certified nerd in high school, I never really knew what the kids were saying even when I was one of them, so "hip" may not be the right word.  Whatever the appropriate vernacular, Yahoo! is doing it for news about black holes - complete with pop culture analogies.  You can see the video here (curse you Yahoo! and your lack of embedding options).  The specific "discovery" they reference was an observation of a peculiar gamma ray burst by the SWIFT satellite, which is a pretty amazing bit of science and certainly worthy of mention.  Besides, everybody likes black holes due to their position on the top of the cosmic sexiness ladder.

As someone who once hoped to model almost exactly what was observed, I have to say that Yahoo! did a decent job with the science.  Sure, they make it sound like we have close-up video of the event rather than a brief gamma ray point source and they think astrophysicists wear lab-coats and write "science" on glass plates, but those are forgivable mistakes in my book.  My only two questions are how can we get more videos like this and why for the love of everything holy don't they have an embed option?

JWST on the Chopping Block: AAS Weighs In

As I previously posted, it looks like the James Webb Space Telescope faces an uphill battle just to avoid the scrap heap.  Today the American Astronomical Society released a statement on the proposed cancellation of JWST.  To no one's surprise, the statement is strongly in favor of continuing JWST, making the argument that "Too many taxpayer dollars have already been spent to cancel the mission now; its benefits far outweigh the remaining costs", in addition to the more standard arguments about preserving jobs, maintaining America's leadership in space technologies, and the benefits to scientific research.

Essentially, I think the single most compelling argument for JWST is the "only way out is through" line of thinking.  We've already spent over $3 billion on this thing, so we're pretty heavily invested.  Additionally, the Hubble Space Telescope was 7 years late, cost three times as much as projected, and has been worth every penny, so there is precedent for this sort of situation working out well in the end.

James Webb Space Telescope on the Chopping Block?

The House Appropriations committee released it's preliminary 2012 budget for "Commerce, Justice, and Science" and the news for science at NASA is not pretty.  From the committee's press release:

"The budget includes... $4.5 billion for NASA science programs, which is $431 million below last year's levels.  The bill also terminates funding for the James Webb Space Telescope, which is billions of dollars over budget and plagued by poor management."

NASA originally proposed a lunch date of 2011 and a total cost of $1.6 billion.  Current estimates place the expected launch date in 2018 at the earliest with a price tag of over $6.8 billion.  With government finances getting tight and everybody in Washington in a budget-cutting mood.  It looks like the next of NASA's flagship science missions might never make it off the ground.

Beautiful Night Skies in Very Dark Places

The Cerro Paranal region of Chile is home to the European Southern Observatory's Very Large Telescope (which is actually four 8.2-meter telescopes) and not surprisingly some of the best conditions for observing the night sky on the planet, as shown in the video below:



Can you find the Magellanic Clouds?  For the real astronomy nerds in the audience, how about 47 Tucanae?

Of course the sky isn't really moving, so here's what it would look like if the camera weren't rotating along with the planet:



Hat tips to APOD and Bad Astronomy

Seeing How Gravity Differs Around The Earth.

I would like to thank Phil at Bad Astronomy for bringing this video to my attention.  It turns out gravity is not felt quite the same around the whole earth.  Fortunately, for the last two years  "ESA's GOCE satellite has gathered enough data to map Earth's gravity with unrivalled precision."

From these gravity measurements the GOCE team was able to produce the above video.  What you see is known as a "geiod" and shows how gravity differs around the earth:

The geoid is the surface of an ideal global ocean in the absence of tides and currents, shaped only by gravity. It is a crucial reference for measuring ocean circulation, sea-level change and ice dynamics – all affected by climate change.

This means (I believe) that if the earth was just an ocean feeling the same varying gravity that exists on our earth, the above video shows how our "ocean earth" would be deformed by these differences in gravitational pull.  As you can see, the effects are very interesting and go a long way explaining why we have different currents and weather patters across the oceans.

Beautiful Saturn Film

Continuing with the cool astronomical images, a number of people have put together this amazing film, which is a composite of images taken from the Cassini spacecraft. Cassini has been in orbit around Saturn since July of 2004.

(5.6k Saturn Cassini Photographic Animation from stephen v2 on Vimeo.)

I just get excited when great science can be not only useful and informative, but also beautiful, artistic and inspiring. Great work.

Another Beautiful Picture Of The Sun.

Alan Friedman does is again.  Thanks to Bad Astronomy for pointing this out.

First Planck Results: The Sunyaev-Zeldovich Effect.

There's been many bloggers writing about the first Planck results presented here at AAS and in Europe but I would like to write a little more than has been written on the Sunyeav-Zeldovich results as I think they are impressive.  Impressive both in terms of the science we get as well as well as this particular example shows how precise CMB experiments have become.  I will focus on the results from this paper.

Okay, what is this effect anyways? The Sunyaev–Zel'dovich effect: "is the result of high energy electrons distorting the cosmic microwave background radiation (CMB) through inverse Compton scattering, in which the low energy CMB photons receive an energy boost during collision with the high energy cluster electrons."  And the thing is, clusters of galaxies are filled with high energy electrons in what is known as the intra-cluster medium (ICM).

This means that we can use specific distortions in the CMB to both locate clusters of galaxies and infer science from them from estimating the Hubble constant to extracting information on the physics driving galaxy and structure formation.

Look at the image above: it shows the precision at which Planck can observe this "SZ" effect.  (And it is just amazing!)  In this image you should note several things.  First, Planck intentionally is observing the sky at many frequency bands to see this stuff. (And watch the frequency change with tie in the image.)  At the lowest frequencies the boost on CMB photons yields a diminished flux, at higher frequencies it is an enhanced flux, and right at 217 GHz there is should be flux.

And if you look closely at the image up top you can see that Planck is seeing this!  The cluster in the center has diminished flux at low frequencies, denoted by the blue smudge,  no flux at 217 GHz and enhanced flux for high frequencies. (Now the smudge turns red.)  So Planck can see this effect really well and the science going into this effect can be studied in detail.

The next two plots to the right show how the mass and luminosity of these clusters relate to redshift. Redshift again being a measure of how far away these objects are from us.   These relations can now be compared to physical models and tell us a lot of science about the universe. Again, what is so great is Planck is seeing a lot of clusters and is able to see how the physical properties of these clusters relate with redshift. (Or as time progressed throughout the universe.)

Now, this stuff is all interesting but the really cool stuff, the main stuff Planck was built for, won't be released until next year. That should be a good day for cosmology and I for one am very excited! Cosmology has become a very precise science indeed!

Come in B-modes.... Come on! :)

The Planck Collaboration. (2011). Planck Early Results: The all-sky Early Sunyaev-Zeldovich cluster sample Submitted to A&A. arXiv: 1101.2024v1

Live From Seattle - ADS Gets an Update

Today the big talks at the AAS were mostly about cosmology, pulsars, and other things that as far as I know were not hot news, but I did find out about one great new thing:  ADS is getting a facelift.  For those of you that don't use it religiously, NASA and the Smithsonian Astrophysical Observatory have for the past 20 years run the Astrophysical Data System, which is an online library for publications in astronomy and astrophysics.  ADS is an invaluable resource for those of us in the astrophysical community, but it also has had the same search interface for the past 20 years.  For those of you that remember searching online in the 90's, the search interface may cause post-traumatic flashbacks.

If you just had a flashback to Lycos, click here and take a good hard look.

So what does the new ADS look like?  Here's the search interface:

Note that like almost all search engines of the past decade they've gone to a single entry box capable of accepting anything from keywords to author names to publication dates.  They've also added six default search modes.  Three just make sense (sort by date, relevance, or citation count) and three are new and very handy (sort by popularity, most referenced, and those most instructive).  The popular option returns those entries with the most recent traffic, the most referenced returns the papers most cited by the most relevant papers, and the most instructive option returns those papers that are most cited by the most cited papers - which is a clever way to favor review articles.

Let's try searching for review articles about the solar dynamo and see how it does.

The results look great.  I have read and highly recommend all but entry #5 as quality reviews of the source of solar magnetic fields - and even though I wasn't previously familiar with entry #5 a quick look leads me to think the problem is with me and not ADS.

Overall, I give the new version of ADS two big thumbs up.  Check it out.

Live From Seattle - Kepler Rocks

The big news from the first day of the AAS can be summed up with "Kepler 10b", which is the first confirmed Kepler planet that's mostly made of rock.  It's also the smallest exoplanet ever found at 4.6 earth masses.  Talks today by many of the Kepler science team focused on this little ball of burning hot rock which orbits its parent star roughly every 12 hours.  This suicidally close orbit leads to surface temperatures in the ballpark of 2500 K, which means it probably looks a lot more like a super-Mercury than a super-Earth.  One scientist compared the newly discovered planet to Dante's Inferno.  You can read the media articles here, here, and here.

From a planet formation standpoint this little guy is also a big deal because it is significantly more dense than Earth, Venus, or Mars, meaning that it is either 75% iron or it contains some material in its core that is so dense it doesn't exist in our solar system.  Laboratory experiments are starting to show that at the ridiculously high pressures one might find in a planet like this one you can get some really funky phases of common materials - things like metallic hydrogen or super-dense ice at 2000 degrees.  It turns out that rocky exoplanets might help us understand high-pressure physics in ways that are really tough to do here on earth.

Live From Seattle - It's the AAS!

Today is the start of the scientific program here at the 217th meeting of the American Astronomical Society and somewhere in days of scheduled talks, posters, receptions, and informal chats we'll try to bring you some of the highlights of the biggest meeting in astronomy and astrophysics.

Also, for those of you in Seattle, the first ever Eternal Universe Nerdfest is going to happen.  Possible days and times include lunch Tuesday, Wednesday, or Thursday, or dinner on Tuesday.  I vote for some seafood (it's Seattle), but the location is up for discussion as well.  If you're interested vote for a time and place in the comments and we'll see what works best for everyone.

The Effects Of Special Relativity On Planetary Orbits.

General relativity affects the orbits of planets in ways Newtonian gravity cannot account for. Interestingly, Lemmon and Mondragon explore if special relativity can account for the same behavior predicted by general relativity.   They find that qualitatively it can, but quantitatively it comes up a little short and so the full general relativistic treatment is still needed.

First a reminder: Precession:  Let's remind ourselves the effects coming from general relativity.  The first is the precession of the orbit demonstrated for Mercury in the image above.  The dotted curve shows what is expected from Newtonian gravity alone: an obit that stays fixed in an elliptical shape forever.  The solid line shows how this changes with general relativity: the orbit moves or precesses over time around the sun.

It may help to consider the gyroscope on the right: if you were to put a red dot on the edge of the spinning disk, and watched above, you would not see that it only traces out a circle as it spins, but a precession pattern like the one in the plot above.

Second reminder: A shrunken orbit:  The second effect general relativity makes is that of shrinking the orbit, illustrated in the plot above again for Mercury.  This is an image of Mercury's potential energy.  Planets want to minimize their potential energy and therefore, like a ball on a hill, "roll to the bottom" of their potential.  As can bee seen, the bottom of the potential for Newtonian gravity is at a larger radius than for general relativity.   Therefore, general relativity forces planets to have a smaller radius.

Note: Both of the effects above have been verified experimentally and are major reasons why general relativity was embraced in the first place.

But is full general relativity really needed? Turning back to the paper, the authors decide to work out these effects in special relativity alone.  First, we start with precession.  Using special relativity alone you get:

Where G is the gravitational constant, c is the speed of light, a is the semimajor axis and e is the eccentricity.  This rate of precession is equivalent to 7.16 arcseconds per century.  This should be compared to precession predicted by general relativity which is 43 arcseconds per century.  Therefore, special relativity undershoots by a factor of 6.

And what about the radius? For special relativity the change in radius is a similar story and becomes:

where 1/2ε is the correction. General relativity gives a correction of 3ε, and so therefore again special relativity comes up short by the same factor of 6.

Always the same factor of 6 huh? I guess so, and I don't off of the top of my head know why it should always been a factor of six.  Anyways, despite being off by this factor, it is very interesting that special relativity predicts the same qualitative behavior as general relativity which is absent in Newton.  Furthermore, since calculations in special relativity are significantly simpler than for general relativity, this special relativistic calculation is ideal if you are just trying to give a qualitative picture of what effects are relativistic.  Perhaps a good one for undergraduates?

Anyone want to take a stab at why it is always a factor of 6???
You can in the comments. :)

Tyler J. Lemmon, & Antonio R. Mondragon (2010). First-Order Special Relativistic Corrections to Kepler's Orbits Submitted to American Journal of Physics arXiv: 1012.5438v1

Bored? Why Not Find a Planet?

Most of you have probably seen volunteer distributed computing projects like Einstein@Home or SETI@Home which use the time your home computer is idle to process data looking for gravitational waves or extra-terrestrial life, respectively.  These are both ways to get additional computing resources for projects that can use all the computing power they can get, and outreach activities that help people contribute to state-of-the-art science.  In that spirit, a collaboration including Yale, Oxford, and the Alder Planetarium is using NASA's Kepler mission to ask for even more interactive help from anyone with an Internet connection, a set of eyes, and some spare time.  The project is called PlanetHunters.org and this is how it works:


After a very brief registration, you can look at actual data from one of the roughly 150,000 stars Kepler monitors and start trying to visually identify transits.  Of course the Kepler science team is also running this data through very sophisticated pattern recognition software to try to identify transits in an automated fashion, but in some ways the human brain is still a better pattern recognition system than even the best computer algorithm.  The only way human eyes can look at years of data from 150,000 stars is if you have a lot of eyeballs, so enlisting the general public seems like a very good idea.

UPDATE:  I beat the New York Times on this one.  They have an excellent article about distributed science projects via the web that you can read here.

What do you think about this?

I just wanted to get people's reaction to something I came across called The Kolob Theorem (links to a pdf). You may have heard about this before, or maybe not. I think the first time I saw this I was at my wife's grandparents' house and I was rather surprised (and a little upset) when I saw the book. It is an absolute hatchet job of astronomy and the worst part is that no one except professional astronomers would even realize how bad a job the author has done with the astronomy.

So take a look at it and give me your thoughts on it (and try not to let my negative comments affect your perception of it). Let me know what you think of the astronomy and whether or not he got any of it right (my personal opinion is very, very no), but don't let my opinion bias your assessment. I have also written a little more of my thoughts on the matter at my personal blog. In my own comments I did not mention anything about the religious aspect, I confined myself to the (bad) astronomy, and I think that we should do the same with our comments. So I propose sticking to the astronomy, and the usefulness (or danger) of someone writing something like this, and what would be the best way to respond to things like this.

Again I don't want to debate the religious aspect, just the sagacity of mixing armchair astronomy with religion.

Also, if someone were to approach you with a manuscript like this, how would you respond (it's a little late for us, since the book was published back in 2005. You can actually buy a copy at Deseret Book.)?

(OK, going back at looking at the comments I wrote on my personal blog, I think I was a little harsh. It's just that I get a little touchy when people mix pseudo-science with my religion.)

Our Beautiful Sun

Astronomy has its disadvantages but the beauty of its images sure isn't one of them.

Click to embiggen.

Hat tip to APOD and Italy.

Some Amazing Time-Lapse Videos

There are some great videos by Tom Low, "the winner of the 2010 Astronomy Photographer of the Year award" pointed out by various blogs showing some amazing timelapse photography.  Below are a few of his videos.

Enjoy! :)


TimeScapes: Rapture from Tom Lowe @ Timescapes on Vimeo.



Timelapse Crane Unleashed from Tom Lowe @ Timescapes on Vimeo.


Timelapse: Nightscapes from Tom Lowe @ Timescapes on Vimeo.

Academically I'm Issac Newton's 14th Great-Grandson

Everyone loves to feel a personal connection to history.  If the subject of Native Americans ever comes up around my wife's family all present will be told that they are direct descendants of Pocahontas.  My ancestors' last name used to be Neilson, which is Danish, but they anglicized it to Nelson when they arrived in America.  Now thanks to the American Mathematical Society and some mathematicians at North Dakota State University, academics can so the same.  The AMS and NDSU's math department have combined forces to produce the Mathematics Genealogy Project - an online, search-able database of mathematicians and like-minded physical scientists with over 145,000 individual entries of mathematicians and scientists dating back to the 14th century.

My adviser's degree is in applied math (as far as I can tell British universities call theoretical physics applied math), so I have a link into the system.  Here are a few of my more notable direct academic ancestors:

G.I. Taylor (2nd Great-Grandfather):  Experimentally showed that the inference pattern of photons passing through a double-slit set-up persisted even if only 1 photon was present at a time; one of the early pioneers in turbulence research; famously calculated the yield of the first atomic bomb from a photo on the cover of Life magazine to within 10% (to the annoyance of the US government, who had kept the yield secret)

J.J. Thompson (3rd Great-Grandfather):  Discoverer of the electron (for which he won the 1906 Nobel prize) and isotopes; inventor of the mass spectrometer; proponent of the delicious-sounding "plum pudding" model of the atom, which was tragically later shown to be inaccurate

John William Strutt, 3rd Baron Rayleigh (4th Great-Grandfather):  Discoverer of argon (for which he won the 1904 Nobel Prize) and Rayliegh scattering, which explains why the sky is blue and the sun is yellow; invented the Rayleigh number, a dimensionless fluid parameter which controls the onset of convection; figured out how human ears use phase differences in sound waves to tell where a sound originates

Issac Newton (14th Great-Grandfather):  Inventor of calculus and Newton's laws of motion; discoverer gravity in the scientific sense; invented and built the first reflecting telescope; originator of the corpuscular theory of light and the concept of lumineferous aether because not even Newton could get everything right

Galileo Galilei (17th Great-Grandfather):  Inventor of the telescope; Father of the scientific revolution; had a little misunderstanding with the Pope; discoverer Jupiter's 4 largest moons, the phases of Venus, and sun spots (although their are some indications that Chinese astronomers beat him to it by looking directly at the sun with their bare eyes)



Like I said, everyone likes to feel a connection to the past and then tell everyone else about it.